This relates generally to MEMS reflective devices, such as digital micromirror devices (DMDs), to project light for illumination. Applications of DMD projection include automotive headlamps, projection displays, spotlights, flashlights, aircraft lamps, marine lamps and other illumination and light beam applications (e.g., event lighting and stage lighting).
In certain applications, beam shaping and adaptive beam control are needed and/or desired in the projected light of an illumination system. In an example automotive application, the beam from an automotive headlamp should, if possible, bend to adapt the path ahead with the forward motion of the automobile. In this manner, the illumination beam will illuminate the path around curves so that the light beam illuminates the path the automobile is going to traverse. This is not possible with a fixed position headlamp. Further, the automobile headlamp should direct light away from oncoming traffic (or be “glare-free”) while maintaining bright illumination for the driver. Conventional systems require the driver to turn OFF the high beam and rely only on lowered illumination (“low beam”) when on-coming traffic approaches, or risk blinding the on-coming drivers due to glare in the eyes of the on-coming drivers.
FIG. 1 is a block diagram of an example conventional automotive headlamp system with beam steering. In FIG. 1, in a headlamp system 10 a conventional illumination source 14 such as a sealed beam lamp is mounted on a swivel that is driven by a motor 16. A control 18 receives inputs from the steering system, a vehicle speed sensor, and a vehicle height sensor, and the lamp 14 is pointed mechanically as the vehicle turns and moves. This conventional approach requires motors and moving parts in the automotive headlamps, making maintenance and repair more frequent and replacement very expensive. Further, the conventional approach illustrated in FIG. 1 often still requires the driver to operate the lamp in a “high beam” and “low beam” mode to adapt the beam to a “low beam” position when on-coming traffic approaches.
Another conventional approach to providing headlamps is to use DMD devices. Lighting with DMD projection offers the opportunity to provide bright and adaptive lighting solutions for many applications. Because the DMD array is “pixel addressable,” the projected beam of light formed with a DMD device can be adaptively shaped to suit a variety of needs. For example, control circuitry can be used to adaptively shape the beam of light projected so as to avoid the eyes of oncoming drivers. Sensors and control circuitry can be used to automate this “glare free” function.
FIG. 2 is a block diagram of a conventional DMD illumination system using a DMD device. The system 20 of FIG. 2 is presented to further illustrate the problems of conventional approaches. In system 20, a single light source 21 and illumination optics 23 are used to direct light from the light source 21 onto the face of the mirrors 24 within a DMD device 22. The DMD device 22 is formed by micro-electromechanical system (MEMS) technology which is based in part on semiconductor device processing. A semiconductor substrate 26 is processed using semiconductor processing steps such as photolithography and other steps including deposition, patterning, etching and metallization steps. An array of micromirrors 24 is formed over the substrate 26. In an example process the micromirrors 24 are formed of aluminum and are mounted on a hinged mechanism. The micromirrors 24 are attached on a hinge and can be tilted using electronic signals applied to electrodes that control a tilt by pivoting the micromirrors about an axis. In an example DMD device, thousands and even millions of the micromirrors are formed in an array that forms a VGA, 720p or 1080p or even higher resolution imaging device, for example. When used in a lamp application, individual micromirrors 24 are positioned to reflect the light from the illumination optics 23 to a projection lens 28 and as shown in FIG. 2, a beam of light is projected out of the system 20.
The micromirrors 24 in FIG. 2 have three individual states, a first “on” state; second a flat or parked state, and finally an “off” state. In the “on” state, the micromirrors 24 in FIG. 2 are tilted in a first tilted position from the flat position, due to signals on an electrode that cause the hinge to flex, and in system 20 the micromirrors 24 are positioned to reflect incoming light from illumination optics 23 outwards to the projection lens 28. In the “off” state, the micromirrors 24 are tilted in a different tilted position to reflect the light away from the projection lens 28. A thermal “light dump” (not shown in FIG. 2) can be provided to collect the light not projected by the lens 28. By varying the tilted positions using electrical control signals, the micromirrors 24 can be used to direct light to the projection lens 28 or the reflected light can be reflected away from the projection lens 28. In addition to the “on” and “off” tilted positions, the micromirrors can be placed in a “flat” state. The flat state is a safe position the mirrors take when no power is applied to the DMD device.
FIG. 3 is a block diagram of the operation of a micromirror in a DMD projection system. In FIG. 3, in a projection system 30 a single illustrative micromirror 38 illustrates the various positions used for the micromirrors. In the “on” state, the micromirror 38 is at a first tilted position, for example at +12 degrees from the vertical or flat position. The illumination source 36 is angled at −24 degrees from the zero degree position, which is aligned with the projection lens 34. Because in reflection from a mirror, the angle of incidence (AOI) of the incoming light is equal to the angle of reflection (AOR) of the reflected light, for a +12 degree tilt, the −24 degree angle for the illumination source results in reflected light at the zero degree position as shown in FIG. 3. The cone of reflected light labeled “on state energy” shows the reflected light directed outwards from the micromirror 38 at the zero degree position. Other DMD devices may provide different tilt angles, such as +/−10 degrees, or +/−17 degrees. When the micromirror 38 is in the “on” state, the light from the illumination source 36 is reflected as the cone of light labeled “on state energy” at zero degrees into the projection lens 34. The projected light is then output from the system 30. The micromirrors can also be put in a “flat” state position, when the system is not powered, and the micromirrors can also be put in an “off” state. In the “off” state position, the micromirror 14 is at a second tilted position at an angle of −12 degrees from the flat position, and in the “off” state the light that strikes the micromirror is reflected away from the projection lens 34, and is not output from the system 30 but instead is output into a light dump 32. In conventional projection systems the flat position of the micromirror 38 is not used when power to the system is applied, but is instead used when the system is not powered. The flat position is sometimes referred to as a “parked” or “safe” position for the micromirror 38.
In forming an adaptive beam, certain of the mirrors in a DMD array can be tilted to the “off” position while other mirrors are tilted to the “on” position and reflect light to the projection lens. In this manner it is possible to shape the beam of light projected by the lens in FIG. 3. However, the mirrors in the “off” position direct light away from the lens, which is inherently inefficient, in that the light provided by the illumination source is only partially utilized. The unused light is directed to a “light dump” which collects it as thermal energy that then must be dissipated. Using a conventional illumination source with a DMD, even when the DMD is operated to adaptively shape the projected beam of light, is therefore inherently inefficient.